Synthesis of Ultrathin Topological Insulator ß-Ag2 Te and Ag2 Te/WSe2 -Based High-Performance Photodetector.

ß-Ag2 Te has attracted considerable attention in the application of electronics and optoelectronics due to its narrow bandgap, high mobility, and topological insulator properties. However, it remains a significant challenge to synthesize 2D Ag2 Te because of the non-layered structure of Ag2 Te. Herein, the synthesis of large-size, ultrathin single crystal topological insulator 2D Ag2 Te via the van der Waals epitaxial method for the first time is reported. The 2D Ag2 Te crystal exhibits p-type conduction behavior with high carrier mobility of 3336 cm2 V-1 s-1 at room temperature. Taking advantage of the high mobility and perfect electron structure of Ag2 Te, the Ag2 Te/WSe2 heterojunctions are fabricated via mechanical stacking and show an ultrahigh rectification ratio of 2 × 105 . Ag2 Te/WSe2 photodetector also exhibits self-driven properties with a fast response speed (40 µs/60 µs) in the near-infrared region. High responsivity (219 mA W-1 ) and light ON/OFF ratio of 6 × 105 are obtained under the photovoltaic mode. The overall performance of the Ag2 Te/WSe2 photodetector is significantly competitive among all reported 2D photodetectors. These results indicate that 2D Ag2 Te is a promising candidate for future electronic and optoelectronic applications.

Building Block-Inspired Hybrid Perovskite Derivatives for Ferroelectric Channel Layers with Gate-Tunable Memory Behavior.

Ferroelectric photovoltaics driven by spontaneous polarization (Ps ) holds a promise for creating the next-generation optoelectronics, spintronics and non-volatile memories. However, photoactive ferroelectrics are quite scarce in single homogeneous phase, owing to the severe Ps fatigue caused by leakage current of photoexcited carriers. Here, through combining inorganic and organic components as building blocks, we constructed a series of ferroelectric semiconductors of 2D hybrid perovskites, (HA)2 (MA)n-1 Pbn Br3n+1 (n=1-5; HA=hexylamine and MA=methylamine). It is intriguing that their Curie temperatures are greatly enhanced by reducing the thickness of inorganic frameworks from MAPbBr3 (n=∞, Tc =239 K) to n=2 (Tc =310 K, ΔT=71 K). Especially, on account of the coupling of room-temperature ferroelectricity (Ps ≈1.5 µC/cm2 ) and photoconductivity, n=3 crystal wafer was integrated as channel field effect transistor that shows excellent a large short-circuit photocurrent ≈19.74 µA/cm2 . Such giant photocurrents can be modulated through manipulating gate voltage in a wide range (±60 V), exhibiting gate-tunable memory behaviors of three current states ("-1/0/1" states). We believe that this work sheds light on further exploration of ferroelectric materials toward new non-volatile memory devices.

Infrared Interlayer Excitons in Twist-Free MoTe2/MoS2 Heterobilayers.

Excitonic devices based on interlayer excitons in van der Waals heterobilayers are a promising platform for advancing photoelectric interconnection telecommunications. However, the absence of exciton emission in the crucial telecom C-band has constrained their practical applications. Here, this limitation is addressed by reporting exciton emission at 0.8 eV (1550 nm) in a chemically vapor-deposited, strictly aligned MoTe2/MoS2 heterobilayer, resulting from the direct bandgap transitions of interlayer excitons as identified by momentum-space imaging of their electrons and holes. The decay mechanisms dominated by direct radiative recombination ensure constant emission quantum yields, a basic demand for efficient excitonic devices. The atomically sharp interface enables the resolution of two narrowly-splitter transitions induced by spin-orbit coupling, further distinguished through the distinct Landé g-factors as the fingerprint of spin configurations. By electrical control, the double transitions coupling into opposite circularly-polarized photon modes, preserve or reverse the helicities of the incident light with a degree of polarization up to 90%. The Stark effect tuning extends the emission energy range by over 150 meV (270 nm), covering the telecom C-band. The findings provide a material platform for studying the excitonic complexes and significantly boost the application prospects of excitonic devices in silicon photonics and all-optical telecommunications.

Van der Waals Heterojunction Based Self-Powered Biomimetic Dual-Mode Sensor for Precise Object Identification.

The design and fabrication of materials that can concurrently respond to light and gas within the dual-modal recognition domain present a significant challenge due to contradictory structural requirements. This innovative strategy introduces a type-I heterojunction, combining the properties of Sb2Te3 and WSe2 nanosheets, to overcome these obstacles. The heterojunction is prepared through a precise stacking approach to create a single-side barrier on the valence band and a near-zero offset on the conduction band. The resulting Sb2Te3/WSe2 heterojunction demonstrates unparalleled performance, showcasing the best integrated photoelectric and gas sensing performance in a single device to date. Based on the above features, the heterojunction successfully integrates visual and olfactory sensing performance, achieving the first biomimetic visual-olfactory dual-mode recognition in a single device. This simulation increased the accuracy of distinguishing electric and fuel-powered cars from ≈50% to ≈96%. This work introduces a novel approach to creating efficient, self-powered sensing materials, paving the way for next-generation biomimetic dual-model devices with broad applications in environmental protection, medical care, and other fields.

Interfacial engineering of tungstic disulfide-carbide heterojunction for high-current-density hydrogen evolution.

Developing low-cost and high-efficiency electrocatalysts to electrolyze water is an effective method for large-scale hydrogen production. For large-scale commercial applications, it is crucial to call for more efficient electrocatalysts with high-current density (≥1000 mA cm-2). However, it is challenging to simultaneously promote the large-scale production and hydrogen evolution reaction (HER) activity of these hydrogen catalysts. Herein, we report the large area tungstic disulfide-carbide (W/WS2-WC) heterojunction electrode vertically grown on an industrial-grade tungsten substrate by the solid-state synthesis method. The W/WS2-WC heterojunction electrode achieves a low overpotential of 473 mV at 1000 mA cm-2 in alkaline electrolytes.